In recent years, devices capable of detecting a gaze direction of a user on the basis of an image including a captured user's eye is miniaturized. Therefore, such devices capable of detecting a gaze direction of a user can be mounted in various apparatuses. Then, applications utilizing the result of a gaze detection of a user with such a device has been studied (e.g., refer to International Patent publication No. 2011-158511).
For example, an instruction input device described in International Patent publication No. 2011-158511 detects a first direction in which a user looks and a second direction in which the user performs a pointing operation. The instruction input device calculates a gaze position of the user on a screen on the basis of a position of the user and the first direction, and calculates a reference line in the space, the reference line corresponding to the gaze position and connecting the user and the screen. The instruction input device calculates a distance, in a second direction, between input coordinates indicating a position of a user's hand and the reference line, as an offset amount corresponding to the gaze position. The instruction input device then calculates a position at which a distance from the gaze position in a first screen specifying direction is the offset amount on the screen, as a pointer display position. The instruction input device combines a three-dimensional direction of a face and a direction of an iris of the eye in the face to detect a gaze direction in real space, and set the gaze direction as the first direction.
The instruction input device is based on a premise that a user's gaze direction can be detected accurately. However, in general, a true gaze direction deviates from a measured gaze direction per se, i.e., unprocessed gaze direction, and from this reason, it is difficult to detect the user's gaze direction accurately when the unprocessed gaze direction data is used as it is. In view of this, so-called calibration processing is performed in advance in order to detect the user's gaze direction accurately.
However, in some cases, positional relationship between a device for gaze detection and a user at the time of detecting the gaze may differ from positional relationship between the device for gaze detection and the user at the time of executing the calibration processing. Different positional relationship between the user and the device results in different gaze positions on a screen of an apparatus even when gaze directions are the same. In addition, it is complicated for a user to perform the calibration processing each time, and it is not practical.
On the other hand, an algorithm for automatically performing calibration in a gaze direction according to a user's action is proposed (e.g., refer to International Patent publication No. 2010-071928). The algorithm disclosed in International Patent publication No. 2010-071928 monitors a user's gaze direction during execution of a series of tasks in which a user is assumed to gaze an object, for example, execution of an action of selecting or clicking small areas on a computer screen. The algorithm obtains a correlation between a direction assumed and a user's gaze direction, and calculates a parameter of the gaze direction to be used for the user from the correlation.
A gaze detecting device is proposed which generates gaze-direction distribution for each head posture with respect to a person to be measured, and corrects the gaze-direction distribution with respect to a head posture other than a reference position using a calibration parameter for calibrating the gaze-direction distribution with respect to the reference position (e.g., refer to International Patent publication No. 2015-136908).